My uncle passed away and I want setup his iPad for use.

Without the AppleID and associated password, you’ll not be able to disable the [default] Activation Lock. With a copy of the original purchase receipt (showing the device serial number) and the Death Certificate, if you visit your local Apple Store, they may be able to reset/wipe the device and remove the Activation Lock.

If the Activation Lock is active, the device is useless to you and anyone else.

This help article might answer some additional questions for you:

https://www.apple.com/ca/legal/internet-services/icloud/en/terms.html

How to request access to a deceased family member's Apple accounts - Apple Support

There is a lot more involved things to do to gain access to a family member’s iOS device, now.

You need a whole more stuff to gain access/permission to a deceased family member’s Apple ID and password to reset a deceased family member’s iOS device, now.

It is not just a matter of getting a copy of the death certificate and iOS device receipt and serial number, any longer.

Apple changed all of that this past September 2019.

You are quite correct in context of obtaining access to the account of a deceased family member - as data protection legislation (such GDPR etc.) protects the data post mortem.

I believe the OP was asking how to reset the iPad as a new device - for reuse - therefore not seeking access to prior data or accounts. As such, assuming this correct interpretation of the question, advice given is believed to be accurate; in such circumstances, as stated, Apple may (or may not) offer assistance.

The OP stated that they do not know the deceased Apple ID for the iPad.

It is not going to be a simple matter to free this device for their personal use.

I believe you are mistaken on your approach.